(1) Field of the Invention
The present invention relates generally to power sources for electric vehicles and, more particularly, to an integrated rechargeable battery and battery charger control unit for powering electric vehicles.
(2) Description of the Prior Art
Typically, rechargeable batteries, particularly lead acid batteries (for example, flooded calcium, valve regulated, and flooded antimonial batteries), for electric vehicles are made as either stand alone units with a separate charger or as combination units where the battery and charger are contained in the same holding tray. In either case, the battery and charger operate independently of each other. The battery is plugged into the vehicle for discharge and then unplugged from the vehicle and subsequently plugged into the charger to be recharged.
Present battery chargers for such types of batteries are typically designed such that they will always put a minimum amount of charge in a battery regardless of the original state of charge of the battery. That is, they generally charge for a set period of time at full charge before sensing a battery's state of charge and finishing at low charge. Present chargers do not compensate for the state of charge existing on the battery at the time charging commences. Therefore the charger will provide the same amount of charge to a battery which has been 1% discharged as to a battery that has been 80% discharged. As a result, such chargers will overcharge batteries that are not fully discharged. Overcharging causes excessive corrosion and deterioration of the battery.
In the applications for which vehicular batteries are used, such as forklift trucks and general transport vehicles, it is generally inconvenient to have to fully discharge a battery and then fully charge the battery. For most chargers, recharging takes several hours. It would be much more convenient if batteries could be charged to their full capacity regardless of their initial state of charge. That is, whether a battery's charge has been depleted by 25%, 50%, or 100%, it would be more convenient and faster to recharge, returning to the battery only that portion of the charge which has been used.
Vehicular batteries such as lead acid batteries may also be damaged by over-discharge. In the past, this damage has been obviated by the provision of commercially available low voltage indicators which can be fitted to an electric vehicle to warn the operator.
U.S. Pat. No. 3,979,657 discloses a battery monitor for disabling a selected operative function, such as the lift on a forklift, when the battery reaches a predetermined discharge state. U.S. Pat. No. 3,898,547 discloses an electric vehicle battery charger interlock system which prevents a vehicle from being driven while the batteries are being charged, and which prevents activation of the charger until the direct current connection of the battery charger to the electric vehicle is completed.
U.S. Pat. No. 5,144,218 discloses a device for determining the charge condition of a small appliance battery. The device comprises a current-frequency converter which generates pulses of a frequency dependent on the battery charge or discharge current. These pulses are counted and used to determine the battery charge condition. The device further comprises correction means which detects an actual battery charge condition for correcting the charge condition determined by pulses. The disclosure teaches the use of the device with appliances and rechargeable electric shavers.
U.S. Pat. No. 4,912,392 discloses a battery charge state monitor having a charging circuit for charging nickel cadmium batteries of the type used for portable computers. An integrating circuit generates a waveform having a frequency proportional to the rate of charging and discharging of the cells. During initial calibration, the number of pulses generated for an exact known quantity of charge is stored in a microprocessor. During subsequent use and charging of the cells, the counter counts in one direction during charging and in the opposite direction during discharge. Since the frequency of the pulses generated is directly proportional to the rate of charge and discharge, the count of the counter provides an exact indication of the state of charge of the cells.
Thus, there remains a need for an improved charger control apparatus which provides for safe recharge of vehicular batteries, whether fully or partially discharged. Further, there remains a need for such a battery charger control apparatus which can disable selected functions of an associated vehicle when the battery is discharged to a predetermined level and/or while the battery is being charged. There also remains a need for an integrated or combined battery and intelligent charger controller.